Studies of soot formation in flames have performed numerically and experimentally. Currently most well-known soot formation is known as following steps :Details in each step, however, have not yet completely understood because of its complexity. The recent major interest is focused on step 2 because some PAHs are reported as spontaneously cancer-induced species. Therefore, in related to the understanding of soot formation, the formation of PAH must be understood in the first place. Objective of this research projects is basically based on this point. In the numerical part, Hai-Wang's chemical reaction mechanism (which consists of nearly 50 species and 500 elementally reactions) is used to predict PAHs and its mole production rate distributions in counter methane-air diffusion flames and double flames. On the other hands, in the experimental part, GC/MS analysis of direct sampled gases from the flames (and LIF technique) were applied to measure the profiles of PAHs distribution of diffusion flames. The numerical results show that there is certain production routes to form Benzene, which is the first form of PAHs, is diffusion flames and C3HX species could controls its process. Moreover, the numerical results underpredict of the production of Benzene. The comparisons of numerical and experimental results suggest that revision of chemical reaction mechanism would be needed to predict, precise, quantitative PAHs data.